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From: Jerry <lanceboyle@qwest.net>
Newsgroups: comp.lang.ada
Subject: Re: How to check a Float for NaN
Date: Wed, 30 Apr 2008 13:36:21 -0700 (PDT)
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On Apr 30, 3:27=A0am, Jerry <lancebo...@qwest.net> wrote:
> How would one check a Float or Long_Float if it has value NaN? The
> only ways that I can come up with are to import a C function (isnan, I
> think) or to write Long_Float'image(Some_Float) to a string and
> examine the first three characters to see if they are "NaN" (and that
> seems to be a GNAT implementation choice so might not be portable,
> which is OK for my use).
>
> Jerry

Check this out:

function Is_NaN(x : Long_Float) return Boolean is
begin
    return x /=3D x;
end Is_NaN;

A couple of minutes on Wikipedia saves the day. From
http://en.wikipedia.org/wiki/NaN#NaN_encodings:

"A NaN does not compare equal to any floating-point number or NaN,
even if the latter has an identical representation. One can therefore
test whether a variable has a NaN value by comparing it to itself."

Jerry